Non-equilibrium molecular dynamics study of shock structure and gas-surface scattering in hypersonic dense argon

Abstract Shock waves and gas-surface interactions are important in aerospace propulsion, hypersonic flight, high energy density physics, and planetary entry. This study uses non-equilibrium molecular dynamics to simulate a nanoscale silicon block moving through argon at 2000 m/s and 300 K over 5-20 atm, resolving both the shock layer and scattering on the surface. Results show that the shock becomes thinner and steeper as pressure rises. Velocity distributions change from a single upstream peak to a bimodal shape inside the layer and then to a near-wall state dominated by reflected atoms. At the interface, incident and reflected velocity correlations show that tangential components become more isotropic with pressure, and two peaks in the normal component merge. The energy accommodation coefficient (EAC) is nearly independent of pressure, while the tangential momentum accommodation coefficient (TMAC) remains high with weak pressure dependence. An atomic mass study at 10 atm shows that heavier atoms penetrate deeper and interact for a shorter time, giving a slight rise in EAC and a slight drop in TMAC. These findings link shock structure to velocity correlation distributions at the interface and guide boundary models for heat and momentum flux in dense gas flows.